Wavelength division multiplexing (WDM) is seen as an increasingly attractive method of using the full bandwidth available of optical fiber, for example, in the 1.3-1.5 .mu.m low attenuation band. For instance, multiple diode lasers, each having an independent wavelength can be used in a WDM system. An integral component of this type of optical fiber network is a wavelength demultiplexing filter. Important criteria for a suitable wavelength demultiplexing filter includes frequency stability, compactness, tuning time, cost, and compatibility with very large scale integrated (VLSI) circuit manufacturing technology. Currently, no suitable wavelength demultiplexing filter has emerged that meets the above criteria.
Wavelength division filters may be implemented with interferometers. Schemes presently being investigated include these based on Fabry-Perot Interferometers with mechanically-tuned mirror spacings. In one scheme, micro-machined interferometers have been fabricated that consist of parallel silicon membranes with an electrostatically tunable spacing which was described in a publication by S. R. Mallinson and J. H. Jerman entitled, "Miniature Micro Machined Fabry-Perot Interferometers in Silicon", Vol. 23, page 1041, Sept. 1987. A voltage is placed across the parallel silicon membranes which allows them to be moved as a function of the voltage applied forming an optical cavity with a nominal 3.5 .mu.m air gap.
In a paper by X. Xiao et al. entitled, "Fabry-Perot Optical Intensity Modulator at 1.3 .mu.m in Silicon", IEEE Photon. Technol. Lett., Vol. 3, page 230, March 1991, a high-finesse Fabry-Perot resonant cavity is described formed by two silicon dioxide mirrors spaced apart by silicon which is doped to form a p-i-n diode optical phase modulator inside the cavity. The free carriers injected in the p-i-n diode are used to modulate the optical phase of light passing therethrough and, thus, the index of refraction in silicon. The presence of free carriers also creates free carrier absorption. An optical fiber may be positioned above the device normal to the silicon surface and the mirrors of the cavity. The Fabry-Perot cavity functions to convert phase modulation into intensity modulation.